1. Field of the Invention
The present invention relates to an image processing apparatus, an image processing method, and a computer program product.
2. Description of the Related Art
The invention relates to an image processing method and an image processing apparatus for converting input image data acquired by image reading, image capturing, or the like into suitable output image data to be output onto an image output medium through attribute determination. For example, although there is no intention to limit the invention, the invention can be applied to a multi-function printer (MFP) having not only a printing function but also a document reading function, a copy function, and a facsimile function.
Examples of the attribute determination include an image form determination (an image classification determination) for determining whether the image data represents a text document, a photograph document, a text and photograph document, or a white document and a color/monochrome determination (chromatic color/achromatic color determination) for determining whether an image is color (chromatic) or monochrome (achromatic).
MFPs employ an automatic color selection (ACS) technology for determining whether a document is a color document or a monochrome document. Some digital color copiers having only a copy function or ones further having a printer function in addition to a copy function also have the ACS function built therein. Although it is general that the ACS is performed at the time of scanning, there are also patent documents disclosing alternative ways, for example, in which the ACS determination is performed after color conversion into an output space or the ACS determination is performed after a magnification changing process or a filtering process depending on the output. Specific examples of such patent documents are as follows.
Japanese Patent Application Laid-open No. 2005-117290: An area designated by a specific color marker is converted into specified information and the information is output. The designation of an area with the color markers is performed in a predetermined form, and the predetermined form is recognized so as to be performed with a conversion process.
Japanese Patent Application Laid-open No. 2007-325128: When an ACS determination is performed, a magnification is changed according to the output size, and then an image area separating process (including the color/monochrome determination) is performed.
Japanese Patent Application Laid-open No. 2005-168044: After a device color space is converted into a uniform color space, the color/monochrome determination is performed.
Japanese Patent Application Laid-open No. 2007-251835: Included are a first image processing unit that processes and stores read-out images and a second image processing unit that processes the stored images and outputs the stored images.
Japanese Patent No. 3313592: A method of determining the document type of an ink jet document is described.
Japanese Patent No. 3530324: A method of determining the document type of a copied document is described.
Japanese Patent No. 3767210: A color/monochrome determination method for a document including characters on a colored background is described.
Japanese Patent Application Laid-open No. 2000-315258: A method of determining a map document is described.
Japanese Patent No. 3983101: A method of determining a text document, a text and photograph document, and a photograph document; an edge determination; a halftone dot determination; a gray determination; and a color determination (chromatic color/achromatic color determination) are described.
In an image forming process of a full-color copy mode in digital color copiers and MFPs, copy processes relating to four basic colors of Cyan (C), Magenta (M), Yellow (Y), and Black (Bk) are respectively performed, and such colors are copied onto one transfer sheet. In addition, when a copy process of a single-color copy mode is performed, an image of one color is copied onto a transfer sheet by performing one copy process.
Accordingly, in such types of copiers and MFPs, the amounts of toner used in a full color mode and in a single-color mode markedly differ from each other, and thus the cost required for user's copy markedly changes. In addition, since an image copied onto a transfer sheet markedly changes depending on the mode, the user needs to pay attention to switching between the color mode and the single-color mode (representatively, the monochrome mode). Therefore, the user should perform an operation of appropriately switching between the operation modes depending on the type of a document.
In order to resolve the inconvenience in such a type of switching between the modes, known is ACS in which it is automatically identified whether a document is a chromatic document or an achromatic document, and the operation mode of a copy process is automatically switched to a color mode or a monochrome mode in accordance with the result of the identification. However, when the color/monochrome determination in the ACS is erroneous, and particularly when a black-and-white document is incorrectly determined as a chromatic document, the output of the copy process is printed in four color plates of CMYBk. Therefore, the image copied onto a transfer sheet is greatly different from an image expected by the user, and the cost and time required for the copy process increase much. Accordingly, a highly accurate determination is demanded.
In addition, recently, a digital color copier not only is used as a signal unit but also is combined with a facsimile function, a printer function, a delivery scanner function, and the like due to an increase in the compatibility with other devices, and thus it is termed a multi-function printer (MFP). In addition, with increasing capacity and decreasing cost in a recording medium such as an HDD drive, a storage medium having high capacity has been built in the MFP. Thus, an image scanned once or an image that is input from other media can be accumulated in the high-capacity storage medium. Such accumulated images can be read out and re-used for the purposes that are different from those expected at the time when accumulated. For example, if images scanned by the scanner and images transmitted through the delivery scanner function are stored in an HDD, the images can be delivered to a place that is different from a first place or can be printed on paper sheets without reading out the document again by using the scanner. In addition, at the time of scanning, the original copy is replicated at an equal multiplication, and after that, the same document can be output to a paper sheet or the like as a 200% enlarged copy image.
As disclosed in Japanese Patent Application Laid-open No. 2007-251835, needed is a technology of accumulating the data scanned by the scanner to be in the state having high usability (generality or versatility), and reusing the accumulated images. Thus, it can be considered a case where the accumulated image is not used in the form of a simple image in the device space (scanner scanned RGB) but used in the form of a converted image in a certain uniform space (for example, sRGB). By accumulating the images in a uniform space, reuse of the information by using a different model and uniformity of the image quality can be achieved. In order to form a uniform space, for example, since the color correction process converts the device space into a uniform color space, a data compression process and a data expanding process are performed. In addition, by performing a filtering process, sharpening of an image, increasing of the resolving power, a moiré eliminating process, and the like are performed.
However, the above-described process is just a conversion process on the read-out image data (scanner scanned RGB) for image output. Thus, there are problems in that, for example, color deviation due to vibration of the scanner increases by performing an enhancement process or a smoothing process using a filter; the definition of gray balance becomes a definition according to the output destination by performing a color correction process; the definition of black changes for each image quality mode (the text mode, the text and photograph mode, the photograph mode, and the color/monochrome); or the amount of information is decreased by compressing the middle γ characteristics from highlight. As the amount of color deviation increases, a thin color line and a color deviation may be not identifiable from each other, or the definition of black of the gray balance becomes not unique, and thus the definition of the determination of a chromatic color or an achromatic color changes for each definition of a stored image, which causes erroneous determination of the color/monochrome in the ACS. In other words, in general technology, at the time of reading out image data, image processing such as a filtering process and a color conversion process is performed on the read image only for the device such as the scanner, an attribute determination is performed on the image data after the image processing such as the color conversion, and the image data is stored in an HDD or the like. Therefore, there is a problem in that the accuracy of the attribute determination is low.
In addition, when an image is formed by reusing the image data that is determined to be a color image and is stored in the HDD, in a case where an image is formed by eliminating part of the image data such as the case of range designation, enlargement, masking, printing onto a paper sheet having a small size, or the like, although the image forming range is monochrome only, the image data is determined to be color as a whole. Accordingly, a billing process is performed as color data, which is disadvantageous to a user in cost.